This invention relates to a double-acting trailer hitch that requires the use of significantly less tongue weight than is required in previously known trailer hitches and which may be used effectively with trailers having various tongue weights and with tow vehicles having various frame strengths.
During the 1920s and 1930s, trailer hitches began incorporating a hitch ball attached to an extension of the tow vehicle and a ball coupler carried by the forward end of the trailer. The coupler was engaged with the ball so that the tow vehicle could pull the trailer along the highway.
A number of developments, including improved highways, more powerful automobiles and trucks, and the advent of electromagnetic trailer brakes allowed the vehicles and attached trailer to achieve greatly increased highway speeds. These developments also permitted much heavier trailers to be towed. The traditional ball hitch was soon found to be unacceptable for handling such increased speeds and trailer weights. In particular, the rig tended to be very unstable. The most significant source of instability was the upward hinging and toggling that occurred between the tow vehicle and the trailer at the point of the coupling ball. This was especially noticeable during braking. At such times, a portion of the linear momentum of the tow vehicle is converted to angular momentum. This causes the front of the tow vehicle to dip downwardly and the rear of the vehicle to pitch upwardly. In the case of the original ball hitch, the delay in activation of the trailer""s electromagnetic brakes caused the significant weight of the trailer to push against the trailer ball. This tended to push the rear of the tow vehicle upwardly with even greater force. The height of the ball at the top of the hinge point effectively formed a toggle with front axle of the tow vehicle and the rear axle of the trailer. Accordingly, the linear momentum of the trailer was also converted into upward force on the ball. The toggle effect was exacerbated when the rig encountered bumps or dips on the highway. All of this made the traditional ball coupling highly unstable and contributed to serious highway accidents.
To counteract the instabilities of the original ball hitch, the weight-distributing hitch was introduced during the 1950s. Initially, the upward hinging exhibited between the tow vehicle and trailer was addressed by adding weight to the tongue of the trailer proximate the ball. It was determined that xe2x80x9ca tongue weightxe2x80x9d of approximately 10 to 15 percent of the gross trailer weight was generally adequate to prevent excessive upward hinging about the trailer ball. However, simply adding tongue weight was and still is, by itself, an inadequate remedy. This weight must be effectively distributed among the axles of the tow vehicle and the trailer so that the rear of the tow vehicle does not sag and a level, stable ride is maintained. Weight distributing trailer hitches that perform this function have been available for many years.
Notwithstanding their current widespread use, conventional weight distributing hitches still exhibit a number of disadvantages. The forces that these hitches generate to counteract the heavy tongue weight of the trailer tend to exert significant stress on the suspension of the tow vehicle. As a result, trucks, sport utility vehicles and full frame automobiles normally must be used as the tow vehicle. Smaller automobiles without a full frame are generally inadequate to support the force produced by the weight-distributing hitch. Such smaller vehicles normally cannot be used to pull a large trailer, which is equal to or heavier than the tow vehicle.
Moreover, the heavy tongue weights exhibited in present weight distributing hitches can create serious instabilities when the rig is driven at highway speeds. In particular, during a sudden lane change, which may result when the driver takes evasive action, the tongue weight carried by the overhang of the trailer behind the rear axle of the tow vehicle often creates a large X-axis moment transverse to the direction of travel. This moment can cause the tow vehicle and trailer to jackknife or flip. Serious accidents often result from such instability.
Trailer instabilities are inherent at all speeds of travel. At speeds below 40 mph they are usually not yet of such significance as to create unsafe travel. Instability increases as a function of speed of travel. At 50 mph some kind of control must be introduced or it is simply so unsafe that the speed cannot be maintained.
The upper threshold of safe travel of a tow vehicle towing a heavy trailer by means of a ball coupler alone is approximately 35 mph for the heavy trailers to approximately 45 mph for lighter trailers. These figures are approximate. The greater the trailer weight is in proportion to the tow vehicle""s weight, the lower the speed at which the coupled vehicles can safely travel.
The free hinging movement at the trailer ball is also a factor in trailer instability. The height of the trailer ball is another factor, because the higher the ball above the axles of the vehicles, the greater is the upward thrust of the toggle at the ball.
Where the ball pitches upward during tow car braking (and before trailer braking is effective due to the magnet delay) the toggle is increased significantly. A heavy trailer thrusting forward on the rear arm of the toggle is pushing upwardly on the ball lifts the rear end of the tow vehicle which causes dangerous loss of traction on the road surface.
Conventional weight distributing trailer hitches also normally require that the trailer axles be positioned fairly close together and located a significant distance from the trailer tongue. This is needed in order to provide the trailer with the necessary tongue weight. If the trailer axles are positioned close together, optimal trailer stability may not be exhibited.
One known trailer hitch designed for use with relatively lightweight frameless automobiles employs a dolly that is mounted beneath the hitch. The dolly travels along the roadway with the rig and supports the tongue weight without distributing the weight to the tow vehicle. This apparatus is unduly complicated and introduces additional wheels that must engage the highway. A failure of the dolly wheels will render the entire rig inoperable.
In my co-pending patent application U.S. Ser. No. 60/109,285, filed Nov. 20, 1998, I disclose a double-acting, reduced tongue weight trailer hitch that permits the trailer tongue weight to be significantly reduced so that less stress is placed on the springs and suspension of the tow vehicle. At the same time, hinging and toggle action between the tow vehicle frame and the trailer frame are significantly reduced and towing stability is improved. Although the hitch apparatus described in that application is quite effective, I have determined that it is desirable to provide a weight distributing hitch that is even more versatile and which may be used effectively with a wide variety of trailer tongue weights and a similar wide variety of tow vehicles frame strengths.
It is therefore an object of the present invention to provide a trailer hitch in which tongue weight is not a factor in towing stability, thus permitting the use of a significantly reduced tongue weight.
It is a further object of this invention to provide a trailer hitch, which joins the frame of the tow vehicle and the frame of the trailer such that they behave as a single piece along an axis extending in the direction of travel.
It is a further object of this invention to provide a trailer hitch that eliminates the upward hinging and toggle action between the tow vehicle frame and the trailer frame so that significantly improved and more stable towing is achieved.
It is a further object of this invention to provide a trailer hitch that permits the tongue weight to be greatly reduced so that less stress is placed on the springs and suspension of the tow vehicle.
It is a further object of this invention to provide a trailer hitch that reduces the dangerous instability and risk of jackknifing often accompanying evasive maneuvers and sudden lane changes.
It is a further object of this invention to provide a trailer hitch, which exhibits extremely stable operation, but without requiring the use of a heavy tongue weight.
It is a further object of this invention to provide a trailer hitch that minimizes the transverse moment at the trailer ball and resulting instability caused when a tow vehicle and trailer swerve on the highway.
It is a further object of this invention to provide a trailer hitch apparatus that reduces the tongue weight of the trailer so that additional accessories and/or equipment are not required to be mounted to the forward end of the trailer.
It is a further object of this invention to provide a weight distributing trailer hitch that may be used effectively for trailers having a wide range of tongue weights (e.g. less than 300 pounds to 1500 pounds, or even more).
It is a further object of this invention to provide a weight distributing trailer hitch that may be adjusted for stable and effective use in combination with light, medium and heavy tow vehicle frame constructions.
It is a further object of this invention to provide a weight distributing trailer hitch apparatus that employs an effective coil spring dampening system to control and reduce bounce and greatly improve ride stability.
It is a further object of this invention to provide a weight distributing trailer hitch employing an easy to operate cam that adjusts the hitchhead quickly and reliably so that the hitchhead and the drawbar can be coupled and the tongue weight is properly and evenly distributed to the tow vehicle.
It is a further object of this invention to provide a trailer hitch of both the weight distribution kind and the low weight kind which converts the toggling upward force at the trailer coupling (which force is generated by the trailer pushing against the coupling means such as during braking) into a downward force at the coupling and thus causing this force to become a force which increases stability, instead of being a force which increases instability as in previous practice.
It is a further object of this invention to provide control of the angular forces of momentum in the tow vehicle during the short period of early braking which occurs before the electric brakes of the trailer become effective.
It is a further object of this invention to provide a trailer hitch apparatus that improves tow vehicle and trailer stability by employing an X-axis coupling, which is located below the centerlines of the tow vehicle and trailer axles and which does not intersect the Z-axis coupling.
It is a further object of this invention to provide a hitch that significantly reduces the need for heavy tongue weights and redistributes those lesser weights to the axles of the tow vehicle and trailer so that a safer, more stable ride is achieved and less stress is placed on the tow vehicle.
This invention results from a realization that the normally high tongue weights used in weight-distributing trailer hitches may be significantly reduced by employing preloaded, double-acting spring means for dampening the relative movement between the tow vehicles and the trailer about a horizontal (X) axis transverse to the direction of travel. The number of springs may be selected to accommodate tongue weights of less than 300 pounds to 1,500 pounds or more. This invention results from the further realization that tongue weight may be reduced and stability improved by pivotably overlapping the forward end of the trailer and the X-axis coupling and joining the drawbar extension of the tow car hitch to the trailer at a point rearwardly of and below the hitch ball. This enables the tow vehicle and trailer to act essentially as a unified beam, which is controlled by a preloaded spring so that hinging and toggling are eliminated when the rig is driven at highway speeds. Conversely, hinging is allowed to occur between the tow vehicle and trailer when bumps and dips are encountered at low speeds. The overlapping of the drawbar extension and the trailer frame, as well as the use of a preloaded double-acting spring assembly also helps to safely control the force of angular momentum normally generated in the tow vehicle during braking. As used herein, xe2x80x9cdouble-actingxe2x80x9d means that the spring assembly controls both upward and downward motion of the tow vehicle and trailer at their point of interconnection, which is located proximate the rearward end of the drawbar extension significantly behind and below the hitch ball. Finally, this invention results from the realization that a cam mounted to the drawbar extension may be utilized to align the hitchhead and the drawbar for interconnection and to quickly, conveniently and effectively distribute a portion of the tongue weight to the frame and wheels of the tow vehicle.
This invention features a double-acting trailer hitch for interconnecting a trailer to a tow vehicle. The hitch includes a drawbar assembly that is selectively attached to the tow vehicle. A first coupling component is attached to a rearward end of the drawbar. A hitchhead assembly includes a ball element that carries a clevis and is suspended by a ball coupling supported by the trailer. The hitchhead also includes a yoke that is pivotally connected to the clevis by a horizontal pivot that is axially transverse to the direction of travel. A drawbar extension is interengaged with and extends generally rearwardly from the horizontal pivot. A second coupling component is pivotally connected to the yoke along a generally vertical axis. The second coupling component may include means for interengaging complementary means in the first coupling component such that the first and second coupling components are coupled and the drawbar is held at a predetermined axial angle relative to the ground. In particular, cam means interconnecting the drawbar extension and the yoke are adjusted to configure the first and second coupling components such that they may be coupled and to hold the drawbar at the predetermined axial angle. There are also means located rearwardly of the ball component for interconnecting a rearward portion of the drawbar extension to the trailer. Such means for interconnecting include a horizontal pivot that is substantially parallel to the horizontal axis and perpendicular to the direction of travel. The means for interconnecting also include preloaded spring means for dampening movement of the drawbar extension relative to the trailer. While the tow vehicle and trailer travel in a straight line on a relatively level highway, the preloaded spring means resist pivoting of the drawbar extension, and the tow vehicle and frame move forwardly as a single unified structure. When the tow vehicle engages bumps and dips in the roadway, the spring means permit the drawbar extension to temporarily pivot relative to the trailer, until the undulation is crossed. The preloaded spring means then return the drawbar extension to its original condition.
In a preferred embodiment, the first coupling component is fixedly interconnected to the drawbar. The first and second coupling components may include elements that prevent hinging or pivoting movement between the first and second coupling components. For example, the first coupling component may include an upper and a lower hitchpin hole. The second coupling component may include a horn featuring an upper slot or recess and a lower hitchpin hole. The horn may also include a ramp that is connected to the upper slot. The drawbar assembly may be directed against the horn such that the upper hitchpin rides up the horn and drops into the slot of the second coupling component. The lower hitchpin hole of the horn may be positioned at a selected vertical angle relative to the slot (e.g. 2xc2x0, 4xc2x0, 6xc2x0). This angle is chosen to impart a desired angle to the drawbar and thereby a corresponding torsion to the frame of the tow vehicle when coupling is completed. A horn having a desired angle may be installed, removed and replaced as required. After the upper hitchpin of the first coupling component is dropped into the slot, the lower hitchpin hole of the first coupling component is separated from the lower hitchpin hole of the second coupling component by the selected angle. The installer aligns these holes by operating the adjustment cam that interconnects the drawbar extension and the yoke of the hitchhead. By rotating the adjustment cam in a first direction, the lower hitchpin holes are aligned. A lower hitchpin is then inserted through the aligned holes to interconnect the first and second coupling components. The adjustment cam is then rotated in an opposite direction such that the hitchhead tilts forwardly and the selected angle is imparted to the drawbar. This transmits a corresponding torsion to the frame of the tow vehicle.
The second coupling component may include means for adjusting the height of the second coupling component. Such means may include a vertical channel element that is slidably interengaged with the horn. Means may be provided for interlocking the horn in the channel element at a selected height. The height adjustment allows the user to fine-tune the hitch to accommodate differing tow vehicle heights. Additionally, the drawbar assembly may be constructed so that the first coupling component is disposed at an angle to the drawbar. As a result, the drawbar assembly may be inverted to position the first coupling component at differing heights relative to the hitchhead assembly. The drawbar assembly is selectively inverted, depending upon the height of the tow vehicle, so that the first coupling component is held at a height that conveniently interengages the second coupling component carried by the hitchhead.
The spring means preferably include at least one generally helical coil or compression spring and linkage that are interconnected between the rearward end of the drawbar extension and the trailer. Each spring may be disposed in a housing that is mounted in the trailer frame. A single spring may be utilized for relatively low tongue weights; a pair of springs may be employed for medium tongue weights; and three springs may be used for heavy tongue weights. The spring assemblies may be adjustably preloaded to dampen pivoting of the drawbar extension about the horizontal axis by a selected or predetermined amount. The spring assembly may include a connector link that is slidably mounted within the housing and resiliently engaged in each spring. The depending connector link may be pivotably interconnected to a distal portion of the drawbar extension. The spring means minimize the hinging motion or toggle effect normally exhibited between the trailer and the town vehicle and thereby reduce the need for using heavy tongue weights to counteract this effect.
This invention also relates to an improvement in a trailer hitch apparatus that releasably connects the trailer to a tow vehicle, wherein at least the tow vehicle has forward and rearward wheels and wherein the trailer and tow vehicle further include a longitudinal axis that extends generally between the center lines of the forwardmost tow vehicle axle and the rearwardmost trailer axle. The improvement includes a forward hitch portion that is releasably attachable to the tow vehicle. There is a rearward hitch portion that carries an X-axis coupling, which X-axis coupling is attachable to the trailer and disposable below the longitudinal axis, whereby a downward toggle is exerted on the X-axis coupling and, upon braking, the hitch apparatus applies a downward force to the rearwardmost axle of the tow vehicle.
The X-axis coupling may include a coupling pin that is releasably engaged with the hitch apparatus. A dual acting spring assembly may interconnect the X-axis coupling and the trailer. The rearward hitch portion may include a Z-axis coupling that is spaced apart and distinct from the X-axis coupling.